Characteristics of mesoscale convective systems and related precipitation in the three-river-source region of China

Mesoscale convective systems (MCSs) are important air water sources to the Three-river-source (TRS) region known as the "Chinese water tower." Using hourly equivalent blackbody temperature (TBB) data from geostationary satellites of Chinese Fengyun-2 series during the warm season (May-August) in 2005-2020 and an objective algorithm, MCSs in the TRS are divided into meso-alpha (M alpha CS), meso-beta (M beta CS), and meso-gamma (M gamma CS), and M alpha CS and M beta CS are subdivided into larger meso-alpha (LM alpha CS), smaller meso-alpha (SM alpha CS), larger meso-beta (LM beta CS), and smaller meso-beta (SM beta CS). Results show that a high-frequency zone of MCSs in the TRS distributes along the source of the rivers. Most MCSs, except LM alpha CS, develop and dissipate in situ. The interannual variation in MCS frequency exhibits a decreasing trend, especially after 2013, mainly due to the decrease in MCSs in the source region of the Yellow-Lancang River. The occurrence of MCSs peaks in August, but MCSs are most likely to produce precipitation in July and usually generate between 1600-2200 h LST (UTC + 8). The precipitation caused by MCSs to the total precipitation (precipitation ratio, PR) accounts for about 40%; MCS PR is closely related to, and increases with, the horizontal scale of the MCS, with M alpha CS PR being the highest, exceeding 67%. The contribution of MCSs to precipitation is mainly reflected in weak precipitation, smaller than 10.0 mm/h. Most of the maximum precipitation of MCSs appears after MCSs reach their prime, with the maximum lag by M alpha CS up to 2 h. Geographical location (red contours) and terrain height (shading, units: m) of the three-river-source region. image